Don’t know anything about wafers other then to eat em. 12 inch can do a lot I presume?
I came away from my years in GE Semiconductor Products Department with a few two-inch (50mm) wafers, only about maybe about 0.025' (~1 mm) thick. These might have twenty or so devices imaged on them, to be separated later by laser-scribing and breaking them apart. I doubt that a 300mm wafer would have only one CPU imaged on it, Likely several, maybe a couple cm square?
Back in the day, the break-even point of profitability was a yield of about 20% of saleable packaged devices. Now? Just guessing.